Concrete radiation shielding means



nitid tes Patent '0 CONCRETE RADIATION SHIELDING MEANS Lyle B. Borst,Center Moriclles', N. Y., assi'giiorto the United States of Americaa'srepresented by the United States Atomic Energy Commission No Drawing.Application March 3, 1949, Serial No; 79,522

19 Claims. or. 250-103 The present invention relates in general to animproved shielding medium for providing protection from the emanationsof radioactive substances, and more particularly to such a shieldingniediu'mcompr'ising a concrete composition in which there is includedcertain heavy elements.

While radioactive emanations have long been known and used and haveserved many useful purposes, it has been appreciated that there areconsiderable physiological and biological haZards associated with thehandling and use of radioactive materials'. Furthermore, apparatus andequipment often suffer deleterious effects when exposed to the varioustypes of radiation. In recent years, with the greatly increasedutiliia'tion of radiation and radioactive materials, and with thedevelopment of sources of radiation of exceedingl high intensities, theproblem of protection from radiation effects has become extremelyimportant.

The conventional method of affording protection to personnel andequipment against radiation is the provision, between them and thesource of the radiation, of a shield or barrier substantially opaque tothe radioactive emanations. In the past, when radioactivity was utilizedon a small scale and the intensities of the emanations were of acomparatively low y'alue', radiation shielding was satisfactorilyeffected by providing a barrier of a suflicient quantity of anyrelatively dense material, it being well known that a sulllcien't amountof matter of any kind will absorb almost every type of radiation.However, with the advent of the cyclotron, the nuclear reactor, andother devices and processes wherein radiation in enormous quantity andof great energy may be produced, the problem of shielding became a muchmore complicated matter. n such cases practical considerations makedesirable the use of shields of minimum weight, volume, and cost. Thisis especially true in applications in which neutronie reactors are to beemployed for the generation of motive power in airplanes, ships, and thelike, wherein the magnitudes of the weight and bulk of the shieldingwill often be the critical'f'actors in determining the practicability ofthe power unit. It is therefore no longer satisfactory toindiscriminately employ any type of relatively dense matter forshielding.

The efficacy of a material for shielding purposes is determinedprimarily by its efficiency per unit thickness in radiation attenuation.In considering thatthe weight and volume of a shield envelopingaradioactiv'e system increase approximately as the cube of the'shieldingthickmess, with a consequent like exponential increase of otherdependent factors such as size of supporting structures and foundation,total cost, afidthe like, thepa'rtic'ular irn portance of employingshielding of superior efficiency per unit thickness is readilycomprehended. Furthermore,

various operations and processes occurring within shielded regions mustbe effected and controlled by operators and equipment stationed onthesafe side of the shielding; since the difiieulty in performing remotecontrol manip- 2,726,339 7 l atented Dec. 6, 1955 2 ulations generallybecomes greater with increase in distance from the operation beingperformed, thinness of shielding again is a criterion. It has becomegreatly desirable, therefore, that new shielding media of greaterefficiency per unit thickness be provided.

The provision of such media of enhanced efficiency is especiallyimportant in the shielding of neutronic reactors, in view of theincreasing present magnitudes of reactor size and radiation fluX. In thepast, ordinary concrete was commonly used for this purpose, but withreactors of current design, exceedingly thick shields are required ifthis material is employed. However, success in providing a moreefii'ci'ent reactor shielding medium is no simple matter. During theoperation of a neutronic reactor, various types of radiation are emittedwith various energy ranges, depending upon the composition andconfiguration of the reactor and upon its previous operation history.These radiations include alpha particles, protons, neutrons, positrons,beta rays, and gamma rays. Not only do each of these species ofradiation react with matter in a substantially difierent manner, butradiation of a single species may react differently with the same matterdepending on the energy level of the radiation. To constitute animproved reactor shielding medium, then, it is consequently necessarythat a material be capable of performing, in a thinner section, thecomplex function of satisfactorily attenuating simultaneously each ofthe species in a reactors composite radiation spectrum.

The present invention provides such shielding medium of enhancedefiiciency. It has been found to be eminently adapted to thesatisfactory shielding of neutronic reactors. Since neutronic reactorsproduce radiation of substantially all of the biologically andtechnically harmful types in quantity and intensity far in excess ofthat previously obtainable by any other means, it follows that theshielding medium of this invention is likewise effective for shieldingany other source of radioactivity.

One object of the present invention is to provide an improved medium forshielding against radioactivity.

Another object is to provide such a medium which has a greater shieldingefiiciency per unit thickness than prior shielding media.

A further object is to provide such a medium which is particularlyeffective against radiation containing neutron and gamma ray componentsof high energy or high in tensity, such as those emanating from aneutronic reactor. I

Still another object is to provide such a medium which may be compoundedin a plastic condition and easily cast into various configurations. I

Other objects will appear hereinafter. v

The improved shielding medium of the present invention comprisesessentially a solid, hydrogenous, concrete composition containing atleast one element which in the free elemental state is normally solidand has a specific gravity at least as great as 6.5, with at least themajor portion of the total mass of said contained elements beingdispersed in the concrete in substantially the free elemental state.

The composition of the concrete shielding medium is subject toconsiderable variation within the scope of this invention, but isconstituted basically of a 'multiplicity of inclusions of one or more ofthe elements specified above in the form of small masses randomlydispersed throughout a matrix, preferably compounded from ahydro-setting cement. The preferred inclusions comprise metallicelements of the above group, dispersed entirely in the form of freemetal masses, or partially in the form of compounds of such metallicelements or in the form of mineral aggregates containing suchcoinponnds.

The class of shielding elements previously defined includes chromium,manganese, iron, cobalt, nickel, copper, zinc, columbium, molybdenum,ruthenium, rhodium, palladium, silver, cadmium, indium, tin, hafnium,tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, thallium,and lead. While any of the elements in this class, when included in theconcrete composition, is effective in increasing the efficiency of theshielding medium, it has been found that those elements of higher atomicweight which may be added in a relatively'high density are generallymore effective. For employing the medium of this invention for shieldingneutronie reactors and other systems with similar radiation spectra, ithas been observed that the relative effectiveness for the purposes ofthis invention of identical volumetric proportions of inclusions of eachof the shielding elements in the previously defined class may be roughlyapproximated by the relationship:

where:

Z=atomic number of specific shielding element D=specific gravity ofspecific shielding element A=atomic weight of specific shielding elementn=an exponent (of value between 2 and 3 for an ordinary reactorspectrum).

However, from the combined standpoints of 'shielding effectiveness, costand over-all practicality, it is preferable to use iron, lead, chromium,manganese, cobalt, nickel, or copper in the shielding medium of thisinvention.

If, in addition to free elemental inclusions of the shielding elements,a minor portion of these elements is also included in mineral form, suchas granular aggregate, the minerals to be chosen for this purpose shouldpreferably have a relatively high content of the shielding element and arelatively high density. Examples of suitable minerals for this purposeare limonite, galena, hematite, alabandite, anglesite, argentite,arsenopyrite, cobaltite, columbite, hubnerite, litharge, magnetite,mimetite, nicollite, stolzite, and wolframite.

In addition to containing shielding elements from the specified group,it is particularly desirable that the medium of this invention have ahigh content of hydrogen; this may be conveniently incorporated as waterof hydration of constituents of the concrete. Therefore, in compoundingthe matrix of the composition, it is advantageous to employ ahydro-setting cement which retains considerable water of hydration uponhardening. Portland cement has been found to be eminently suited for thepurpose. In utilizing Portland cement, in applications where shieldingefficiency is of paramount importance it is advantageous that the matrixconsist of only cement and water. On the other hand, improved structuralstrength of the concrete may often be obtained, at some cost ofshielding efiiciency, by including in the matrix composition, inaddition a portion of porous granular mineral aggregate. While themineral aggregate utilized in this respect may profitably be sand orgravel, as is conventional in compoundmg ordinary structural concrete,it is in most cases preferable to use a mineral containing one or moreof the previously specified shielding elements. Better still, themineral incorporated in the composition may be such a one which also hasa high content of water of hydration. It has been found that limonite, ahydrated iron ore, is ideally suited for the purpose.

While there is no marked criticality as to the proportlons ofingredients employed in compounding the concrete composltion, it isgenerally very desirable that the relative amounts of materials usedafford as high as practicable an atomic concentration both of theselected shielding element or elements and of hydrogen. How ever, in thepresent composition, an increase in the concentration of one of thesewill ordinarily result in a decrease in the concentration of the other.For high shielding effectiveness, particularly for simultaneouslyshielding against neutrons and gamma rays, it is important that neitherbe excessively increased at the expense of the other. To compoundefficient shielding compositions which are universally adaptable to anyradiation spectrum, it is beneficial to employ atomic ratios of theshielding elements of the present invention to hydrogen within the rangeof 0.1:1 to 10:1. It has been found that within this range, a ratio ofthe order of 1.5:1 gives especially good results, particularly in theshielding of neutronic reactors. High absolute values of atomicconcentrations within this range of relative concentrations mayordinarily be secured by omitting from the concrete compositionaggregate materials, which are ordinarily of relatively low shieldingeffectiveness. Considering generally several concrete compositions ofthe present invention, all containing the same specific shieldingelement and all having the same atomic ratio of such element tohydrogen, the'denser the mass the more eflicient it is as a radiationshield. This increase in efficiency is attained in the present inventionby the provision of concrete shields with atomic ratios within thepreferred range, having densities ranging up to several times that ofordinary structural concrete.

It should be understood in connection with adjusting the ratio of thesaid atomic concentrations that the content of hydrogen in the concretecomposition is generally present substantially entirely as water ofhydration of the mineral components employed. In the setting orhardening of a concrete prepared in the conventional manner, the contentof water of hydration per unit weight of hydratable material usuallyreaches a single constant value, regardless of the amount of excesswater added when mixing the concrete. Therefore, the proportion ofwater, and the resulting hydrogen content of the concrete mayeonsequently be adjusted to the desired value by employing the properpercentages of cement and other hydratable minerals in the mix. Knowingthe concentration of atoms of hydrogen in the concrete to be used for amatrix for the shielding element inclusions, and the desiredconcentration of atoms of the shielding element, the proportions ofingredients for compounding the concrete composition may thus readily becalculated.

To cite some specific examples of the magnitude of the proportions ofingredients in the mix, it has been found that where concretecompositions are compounded of Portland cement, water, and one of theshielding elements in its free elemental form, the ratios of the dryingredients for universally adaptable shielding compositions shouldpreferably be the following for the specific elements listed:

Iron: 0.12 to 12.4 pounds per pound of Portland cement Lead: 0.46 to46.0 pounds per pound of Portland cement Chromium: 0.12 to 11.5 poundsper pound of Portland cement Manganese: 0.12 to 12.1 pounds per pound ofPortland cement Cobalt: 0.13 to 13.1 pounds per pound of Portland cementNickel: 0.13 to 13.0 pounds per pound of Portland cement Copper: 0.14 to14.1 pounds per pound of Portland cement When other shielding elementsor combinations thereof are used, the preferable ingredient ratios areof the same order as those set forth above.

The sizes and shapes of the included shielding elements, in either freeelemental form or in the form of compounds or minerals, are not criticalas long as the sizes of the inclusions are relatively small compared tothe physical dimensions of the shield. For example, in case of shieldsfive to eight feet thick, the inclusions may satisfactorily be as largeas walnuts, while with shields three to five feet thick the massesshould ordinarily be about pea-size or smaller. Generally, as thethickness of the shield increases, the size of the inclusions mayproportionally increase, however it is preferred that inall cases theinclusions be as small as practicable. However, while from thestandpoint of radiation attenuation the inclusions should be as small aspossible so that the composition approaches advantageous homogeneity, ithas been found that the use of masses smaller than about shot-size, suchas powders, filings, and scrapings, generally detracts from thestructural and mechanical properties of the shielding. Any desired shapeof the inclusions may be employed, such as lumps, balls, pellets, discs,cubes, and the like. Very good results have been obtained, particularlywhen employing metallic shielding elements, by the choice ofconfigurations such as small rods, bars, nails, and the like, whichserve to mechanically reinforce the concrete.

The standard of excellence of the raw material ingredients of theconcrete composition should be atleast as high as that set for betterquality structural concretes. The cement used should not have beensubjected to detrimental treatment. For example, in the case of Portlandcement, exposure to moisture and weather should have been avoided. Themineral aggregates used should preferably be comminuted to a granularconsistency and should ordinarily be free of soft, friable, flaky, orlaminated particles. Likewise the water used should be clean and freefrom deleterious foreign substances. As is the customary practice in theart, the ingredients of the concrete with the exception of water shouldbe thoroughly mixed together, and the water subsequently slowly addeduntil the mass has the usual pouring consistency. Then, in accordancewith standard practice, it may be poured into hollow molds, or in anyother suitable manner cast into the desired configuration.

The shielding medium of this invention affords marked improvement overordinary structural concrete in shield ing against any and all types ofharmful radiation, especially in providing protection against gammaradiation of all energies, and against neutrons, particularly those withenergies in excess of about 1 million electron volts. In general, of thevarious species of radiation, gamma rays and neutrons present the mostdiflicult shielding problem. This is especially true in the case of theusual spectrum of radiation emanating from a neutronic reactor. With anordinary reactor spectrum, if sufficient shielding to satisfactorilyattenuate the gamma and neutron emanation is provided, the attenuationof other species of radia tion, i. e., alpha particles, beta particles,protons, and positrons, will normally be much more than is necessary. A-pha particles, beta particles, protons, and positrons, being chargedparticles, are stopped, even when at high energies, in attempting totraverse thicknesses of matter of the order of a few inches. Thethickness of material required for charged particle shielding is roughlyinversely proportional to the density of the material. Since concretecompositions of this invention are more dense than ordinary concrete,many of them having densities several times that of ordinary concrete,they are consequently the more efiicient in shielding against chargedparticles.

The attenuation of gamma and neutron radiation is not so simple as thatof charged particles. As is known, gamma rays, not being true particles,react with atoms of matter by special reactions such as Comptonscattering, photoelectric absorption, and pair production, and hentronsare commonly attenuated by inelastic scattering, elastic scattering, andcapture b'y n'uclei. However, the materials which are significantlyeffective in inelastic scattering and capture are, on the whole, verypoor elastic scatterers, and furthermore ordinarily most deleteriouslyemit secondary gamma radiation upon capturing a neutron. While theseshielding materials are often also good gamma attenuators, it isgenerally the case in neutron shielding that until the transient neutronflux is reduced to insignificance, the individual increments ofshielding generate more gammas than they remove from the transitoryradiation. For example, it has been shown that if it were attempted toshield an ordinary neutronic reactor with a reasonable thickness of ironor lead, the gamma flux leaving the shield would be greater than theentering gamma flux. It had therefore become the customary practice forshielding systems producing high-intensity neutron or neutron and gammaradiation to employ materials,'such as concrete, which, while beingrelatively poor in gamma attenuation, inelastic scattering, and neutroncapture, do not emit secondary gammas to any especially adverse degree.Now, although the medium of the present invention contains materialswhich are particularly effective in all of the mentioned mechanisms ofneutron and gamma attenuation, and so is subject to much secondary gammageneration, yet by its peculiar inate characteristics it is, able toattenuate these secondary gammas in reasonable shield thicknesses.Therefore, by successfully alleviating the secondary gamma problem, themedium of present invention provides a means which takes full advantageof all of the mentioned neutron and gamma attenuating mechanisms, and isthus able to shield with its exceptional efiiciency against radiationhaving neutron and gamma components.

In shielding a neutronic reactor with the medium of this invention ithappens that the magnitude of secondary gamma radiation generated in theshielding is considerably in excess of that of the primary gammaradiation being emanated from the reactor. It has been found that forapplications wherein this troublesome secondary gamma radiation isespecially high, the compositions of this invention may be furtherimproved by the additional incorporation therein of minor amounts ofboron. Boron has an exceptionally great propensity for absorbing slowneutrons and upon doing so it does not ordinarily adversely emit gammaradiation. Thus the presence of a small quantity of boron at any pointin the shield serves to reduce the flux, not only of neutrons, but ofgamma rays as well. The boron may be added, as are the specifiedshielding elements, in the form of free metal inclusions or in combinedforms such as compounds or minerals containing boron. Colemanite, aboron-containing mineral, when finely divided, serves as an ideal formof boron for dispersion in the concrete composition. It is preferable,when any boron is included, that it be in small amounts, such as below5% by weight in the composition; concentrations of about 1% by weighthave been found to be entirely sufficient.

Besides being superior in radiation attenuation to ordinary structuralconcrete, the concrete compositions of the present invention possesssubstantially all of the inci dental attributes of that material as ashielding medium. The present composition is easily prepared, and may besimply cast into virtually any desired monolithic configuration. It isinexpensive and readily handled in conventional industrial concreteapparatus. Shields fabricated from the present medium are able, inaddition to providing radiation protection, to serve as mechanicalstructures for housing and supporting the shielded systems they envelop.Small shielded containers fabricated from the material can be producedso cheaply as to make them very well suited as discardable shippingcontainers for radioactive materials.

In view of the variations which may be effected in the choice ofparticular constituents and the proportions thereof, within thelimitations pointed out herein, in compounding the shielding medium ofthe present invention, further understanding of this invention may berealized by consideration of the following specific examples.

EXAMPLE I 7 Pounds Portland cement; 2660 Steel punchings 5000 (Steeldiscs A" to /1" thick by to l" diameter;

7 While continuing the mixing, water was 'slowly sprayed into the massuntil the concrete was of the consistency conventional for pouring,whence it was poured into prepared molds, rodded, and allowed to harden.The total volume of the hardened concrete was 32 cubic feet, and itsdensity was found to be 256 pounds per cubic foot. The averageconcentration of iron in the mass was 156 pounds per cubic foot. It wascalculated that the concrete retained 532 pounds of combined water, witha resulting concentration of hydrogen atoms of 1.85 pounds per cubicfoot. The iron to hydrogen ratio was therefore 84 lbszl lb., or on thebasis of atomic ratios, 1511.

For purposes of comparison, a batch of ordinary structural concrete wasprepared by mixing 1 part by volume of portland cement, 2 parts byvolume of sand 95 SiOz), and 3 parts by volume of rock 95% CaCOs),adding water, pouring, rodding, and permitting to harden. The density ofthe hardened concrete was found to be 150 pounds per cubic foot.

The samples of each of the two concretes were consecutively substitutedfor a section of shielding surrounding a neutronic reactor and thusexposed to a neutron flux density of the order of neutrons per squarecentimeter'per second, with neutron energies ranging from fission energydown to that of thermal equilibrium with the system, and an accompanyinggamma flux of about 12,000 roentgens per hour. The substitutedshieldsection was centrally located in a fiat planar concrete wall whichshielded one face of a cubical reactor, and was small with respect tothe shield face; the radiation incident upon the samples wasconsequently substantially equivalent to that which would be emanatedfrom a infinite-plane radiation source situated adjacent the inner faceof the shield. The concrete containing iron had been poured in fourequally sized blocks, each 16 inches thick; the blocks were positionedone behind the other, the locus of centers perpendicular to the shieldface, with four-inch spaces between the blocks to permit the insertiontherebetween of radiation-measuring instrumentalities. For each typeconcrete, the relaxation lengths, that is, the distances, measuredperpendicularly away from the source, in which a particular fluxdecreases by a factor of 2.718, were determined for neutrons and forgamma rays, and are presented in tabular form below.

Neutor; (relaxatitzin lengizh s cm. average over 6 Gamma sections) l gleng s Section (cm) erage) Inner 2 3 Outer Concrete containlngiron 5. 596.93 7.33 l 7.33 9.2 Ordinary concrete 1 The slight increase inrelaxation length is presumed due to a corresponding decrease in theproportion of inelastic scattering to total scattering occurring,conforming to a. decreasing percentage ofhigh-cncrgied neutrons in theneutron flux as it traverses the shield.

1 Average of 10.

From these data, the fractions of such incident neutron and gamma fluxwhich will succeed in traversing 4 feet and 6 feet thicknesses ofshielding of each type of concrete were calculated and are tabulatedbelow.

a thickness of 6 feet of theor'dinary concrete. In'other words, toobtain the same shielding protection, a thickness of ordinary concreteof over of that of the composition of this invention is required.

As a measure of the relative mechanical properties of the two types ofconcretes, the seven-day strength in compression of each was determined;the results are tabulated below.

V P. s. i. Concrete with iron 3850 Ordinary concrete 3320 Thecomposition containing iron is thus considerably superior to ordinarystructural concrete in this regard also. I

g EXAMPLE II A shielding sample having a higher iron to hydrogen ratiothan that in Example I was prepared by mixing the following dryingredients in the proportions specified.

Percent by weight Portland cement 13.6 Limonite (Hard chunks, A" to 1")Natural 2Fe2O3-3H2O 27.1

Analysis:

Fe: 50 by weight. Bound H2O: 8-12% Mn: 0.21.0% Steel punchings 59.3

Water was added and the batch was cast in the usual manner. Theresulting concrete had a density of 270 pounds per cubic foot, aconcentration of iron in the composition of about pounds per cubic foot,and an atomic ratio of iron to hydrogen of 2.2:1. When tested as inExample I, the neutron relaxation length averaged about 6.3 centimetersand the gamma relaxation length was found to be between 9 and 10centimeters. The seven-day strength in compression of the sample wasfound to be 3500 p. s. i.

This specific composition was found to have such advantageouscharacteristics from the standpoint of overall practicality that it hasbeen employed with excellent results as the enveloping shield of one ofthe largest neutronic reactors in existence.

EXAMPLE III A sample of a shielding composition of the present inventioncontaining boron was prepared by mixing the following dry ingredients:

Percent by weight Portland cement 32.1 Iron shot (SAE 330; approx. ,5diam; 98%

sorbent, white powder) 3.47

then adding water and pouring into molds. The sample was tested in thesame manner as in the preceding examples. The empirical data aretabulated below.

Atomic ratio, ironzhydrogen 1.5:1

Density 224'lbs./cu. ft. Boron content 0.5% by weight Neutron relaxationlength, average area-s39 and component ratios in compounding'concretecompositions of the present invention are the mixes detailed below. Forsimplicity the data are presented in tabular form, the method ofpreparation and the radiation spectrum to which the relaxation lengthsrelate being the same as in the preceding examples.

Mix A Dry ingredients:

Portland cement 32% by weight. Copper discs /2 diam. 9 10 thick) 68% byweight. Data:

Density 276 lbs/cu. ft. Atomic ratio, copper:hydrogen 1.5:1. Relaxationlengths (average):

Neutrons 6.1 cm. Gamma rays 8.5 cm.

Mix B Dry ingredients:

Portland cement 31.0% by weight. Nickel balls 31.8% by weight. Chromiumpellets 37.2% by weight. Data:

Density 267 lbs/cu. ft. Atomic ratio (nickel-j-chromium):

hydrogen 1.84:1. Relaxation lengths (average):

Neutrons 8.0 cm. Gamma rays 11.5 cm.

EXAMPLE V A. concrete composition containing lead may be prepared bymixing, while dry:

I Percent by weight Portland cement 27.1 Lead shot 72.9

adding water, and casting in the usual manner. The composition will haveapproximately the following physi- There is strong indication that forthe radiation spectrum considered in the other examples, the neutronrelaxation length of this composition would be considerably less than 7cm., and the gamma relaxation length would be less than 9 cm.

For furtherdetails concerning the theory, design, construction andoperations of neutronic reactors, reference is made to the followingUnited States Patent which has issued upon an earlier-filed copendingapplication of the common assignee: U. S. 2,708,656, May 17, 1955, E.Fermi et al., Neutronic Reactor, application Serial No. 568,904, filedDecember 19, 1944.

It is to be understood that the above examples are illustrative only anddo not limit the scope of the present invention as it is intended toclaim the invention as broadly as possible in view of the prior art.

What is claimed is:

1. In a shield for restraining the egress of emanations of radioactivityfrom a neutronic nuclear fission reactor, improved shield meanscomprising a mass of a solid concrete composition compounded from ahydro-setting cement and water, and containing at least one elementwhich in the free elemental state is normally solid and has a specificgravity at least as great as 6.5, said contained elements beingcollectively present in an amount corresponding to an atomic ratio inthe composition of such elements to hydrogen within the range of 0.1:1to 10:1 and the major portion of the total mass thereof being dispersedrandomly in the concrete in substantially the free elemental state inthe form of a multiplicity of masses.

2. In a shield for restraining the egress of emanations 75 to hydrogenof substantially 1.5 :1, with at least the major portion of the ironbeing dispersed randomly in the concrete in substantially the freeelemental state in the form of a multiplicity of masses.

3. In a shield for restraining the egress of emanations of radioactivityfrom a neutronic nuclear fission reactor, improved shield meanscomprising a mass of a solid concrete composition compounded fromPortland cement and water, and containing iron, in an amountcorresponding to an atomic ratio in the composition of iron to hydrogenwithin the range of 0.1:1 to 10:1, with at least the major portion ofthe iron being dispersed in the concrete in substantially the freeelemental state in the form of a multiplicity of masses, there beingalso boron dispersed throughout the concrete in a proportion of not morethan 5% of the weight of the composition in the form of a multiplicityof masses.

4. In a shield for restraining the egress of emanations of radioactivityfrom a neutronic nuclear fission reactor, improved shield meanscomprising a mass of a solid concrete composition compounded from ahydro-setting cement and water, and containing iron in an amountcorresponding to an atomic ratio in the composition of iron to hydrogenwithin the range of 0.1:1 to 10:1, with at least the major portion ofthe iron being dispersed randomly in the concrete in substantially thefree elemental state in the form of a multiplicity of masses.

5. In a shield for restraining the egress of emanations of radioactivityfrom a neutronic nuclear fission reactor, improved shield meanscomprising a mass of a solid hydrogenous concrete composition containingiron, the major portion of the said iron being randomly dispersed in theconcrete in substantially the free elemental state in the form of amultiplicity of masses, and a minor portion of the said iron beingdispersed in the concrete as a multiplicity of masses of a mineral ofwhich iron is a constituent.

6. In a shield for restraining the egress of emanations of radioactivityfrom a neutronic nuclear fission reactor, improved shield meanscomprising a mass of a solid, hydrogenous, concrete compositionconstituted by the hardened admixture of portland cement, a multiplicityof masses containing iron in substantially the free elemental state, amultiplicity of masses of limonite, and water, with the ratio by weightof the said free elemental iron to limonite being substantially 2.221.

7. In a shield for restraining the egress of emanations of radioactivityfrom a neutronic nuclear fission reactor, improved shield meanscomprising a mass of a solid, hydrogenous, concrete compositionconstituted of the hardened admixture of portland cement, a multiplicityof masses containing iron in substantially the free elemental state, amultiplicity of masses of limonite, and water, with the relativeproportions by weight of the said cement, free elemental iron andlimonite being substantially 3:13 :6, respectively.

8. In a shield for restraining the egress of emanations of radioactivityfrom a neutronic nuclear fission reactor, improved shield meanscomprising a mass of a solid concrete composition compounded fromportland cement and water, containing iron, at least the major portionof the said iron being dispersed in the concrete in substantially thefree elemental state in the form of a multiplicity of masses, and alsocontaining boron, in a proportion of not more than 5% by the weight ofthe composition, dispersed as a multiplicity of masses of colemanite.

9. In a shield for restraining the egress of emanations of radioactivityfrom a neutronic nuclear fission reactor, improved shield meanscomprising a mass of a solid concrete composition compounded fromportland cement, water, and copper, with at least the major portion ofthe said copper being dispersed in the concrete in substantially thefree elemental state in the form of a multiplicity of masses.

10. In a shield for restraining the egress of emanations ofradioactivity from a neutronic nuclear fission reactor, improved shieldmeans comprising a mass of a solid concrete composition compounded fromportland cement, water, and lead, with at least the major portion of thesaid lead being dispersed in the concrete in substantially the freeelemental state in the form of a multiplicity of masses.

11. In a shield for restraining the egress of emanations ofradioactivity from a neutronic nuclear fission reactor, improved shieldmeans comprising a mass of a solid, hydrogenons, concrete compositioncontaining at least one element which in the free elemental state isnormally solid and has a specific gravity at least as great as 6.5, atleast the major portion of the total mass of said contained elementsbeing dispersed randomly in substantially the free elemental state.

12. In a shield for restraining the egress of emanations ofradioactivity from a neutronic nuclear fission reactor, improved shieldmeans comprising a mass of a solid, hydrogenous, concrete compositioncontaining at least one element which in the free elemental state isnormally solid and has a specific gravity at least as great as 6.5, atleast the major portion of the total mass of said contained elementsbeing dispersed in the concrete in substantially the free elementalstate in the form of a multiplicity of masses, there being alsodispersed throughout the concrete a minor proportion of boron.

13. In a shield for restraining the egress of emanations ofradioactivity from a neutronic nuclear fission reactor,

improved shield means comprising a mass of solid concrete compositioncompounded from a hydrosetting cement, and containing at least oneelement which in the free elemental state is normally solid and has aspecific gravity at least as great as 6.5, at least the major portion ofthe total mass of said contained elements being dispersed in theconcrete in substantially the free elemental state in the form of amultiplicity of masses.

14. In a shield for restraining the egress of emanations ofradioactivity from a neutronic nuclear fission reactor, improved shieldmeans comprising a mass of solid concrete composition compounded from ahydrosetting cement, and containing at least one element which in thefree elemental state is normally solid and has a specific gravity atleast as great as 6.5, at least the major portion of the total mass ofsaid contained elements being substantially homogeneously distributed inthe concrete in substantially the free elemental state.

15. In a shield for restraining the egress of emanations ofradioactivity from a neutronic nuclear fission reactor, improved shieldmeans comprising a mass of solid concrete composition from ahydrosetting cement, and containing at least one element which in thefree elemental state is normally solid and has a specific gravity atleast as great as 6.5, the major portion of the total mass of saidcontained elements being dispersed randomly in the concrete insubstantially the free elemental state in the form of a multiplicity ofmasses, and a minor portion of the total mass of said contained elementsbeing dispersed in the concrete in mineral form as a multiplicity ofmasses.

16. In a shield for restraining the egress of emanations ofradioactivity from a neutronic nuclear fission reactor, improved shieldmeans comprising a mass of a solid concrete composition compounded froma hydrosetting cement and water, and containing nickel, with at leastthe major portion of the nickel being dispersed randomly in the concrete'in substantially the free elemental state in the form of a multiplicityof masses.

17. In a shield for restraining the egress of emanations ofradioactivity from a neutronic nuclear fission reactor, improved shieldmeans comprising a mass of a solid concrete composition compounded froma hydrosetting cement and Water, and containing chromium, with at leastthe major portion of the chromium being dispersed randomly in theconcrete in substantially the free elemental state in the form of amultiplicity of masses.

18. In a shield for restraining the passage of emanations ofradioactivity, improved shield means universally adaptable to providingprotection against all types of harmful radioactivity comprising a massof a solid, hydrogenous, concrete composition containing at least oneelement which in the free elemental state is normally solid and has aspecific gravity at least as great as 6.5, at least the major portion ofthe total mass of said contained elements being dispersed randomly insubstantially the free elemental state.

19. The shield means of claim 18 wherein said concrete composition iscompounded from Portland cement, and wherein at least one of saidcontained elements is non.

References Cited in the file of this patent UNITED STATES PATENTS1,390,327 Bassett Sept. 13, 1921 1,780,107 Barry Oct. 28, 1930 2,304,391Zimmerman Dec. 8, 1942 2,416,701 Kocher Mar. 4, 1947 FOREIGN PATENTS4,137 Great Britain of 1876 24,618 Great Britain of 1904 233,011Switzerland Oct. 2, 1944 114,150 Australia May 2, 1940 861,390 FranceOct. 28, 1940 OTHER REFERENCES Goldbergerz. The Shielding of NuclearReactors, MDDC-806, U. S. Atomic Energy Commission, March 24, 1947, 9pages. (Copy in Patent Oflice Library.)

1. IN A SHIELD FOR RESTRAINING THE EGRESS OF EMANATIONS OF RADIOACTIVITYFROM A NEUTRONIC NUCLEAR FISSION REACTOR, IMPROVED SHIELD MEANSCOMPRISING A MASS OF A SOLID CONCRETE COMPOSITION COMPOUNDED FROM AHYDRO-SETTING CEMENT AND WATER, AND CONTAINING AT LEAST ONE ELEMENTWHICH IN THE FREE ELEMENTAL STATE IS NORMALLY SOLID AND HAS A SPECIFICGRAVITY AT LEAST AS GREAT AS 6.5, SAID CONTAINED ELEMENTS BEINGCOLLECTIVELY PRESENT IN AN AMOUNT CORRESPONDING TO AN ATOMIC RATIO INTHE COMPOSITION OF SUCH ELEMENTS TO HYDROGEN WITHIN THE RANGE OF 0.1:1TO 10:1 AND THE MAJOR PORTION OF THE TOTAL MASS THEREOF BEING DISPERSDRANDOMLY IN THE CONCRETE IN SUBSTANTIALLY THE FREE ELEMENTAL STATE INTHE FORM OF A MULTIPLICITY OF MASSES.